A pottery or ceramics kiln is an instrument used to convert clay into finished pottery. The conversion is an irreversible process, known as vitrification, that partially melts and fuses clay into glass-like pottery through the application of high temperatures. The temperature required to complete the conversion process depends on the specific clay mixtures used. For a typical stoneware clay, temperatures on the order of 2345° F. are required to complete the conversion process.
Various heating processes exist for vitrifying pottery and ceramics. These include electric heating, natural gas combustion, propane combustion, and wood combustion. Electric processes utilize an oxidizing air atmosphere as the heating elements typically experience short service lives in reducing atmospheres. The combustion processes allow for both oxidizing and reducing atmospheres yielding greater flexibility in glazing operations and in the use of techniques such as salt firing. Wood combustion processes are held in particularly high regard based on the unique characteristics imparted to the fired piece and the renewable nature of the fuel source.
Electric kilns offer the benefit of simplicity of operation and scalability to small sizes suitable for amateur and small scale production uses. Natural gas and propane fired kilns are scalable from small to large size, but require a higher level of expertise to safely operate due to the hazardous nature of these fuels and the significant volumes required to fire a kiln. For this reason, natural gas and propane fired kilns enjoy limited use among amateur and small scale production users. Wood fired kilns offer inherent safety benefits compared to natural gas or propane kilns, but their use has been limited to professional, large-scale operators because of the labor intensive nature of wood firing and the large size and cost of the kilns. Conventional wood kilns are labor-intensive because the firing process requires a large quantity of wood, frequent refueling, and long firing times. For example, a minimum-sized wood kiln might require a cord or more of wood, with small pieces fed every few minutes during peak firing, and a total attended firing time of 24 to 48 hours. The large size of wood kilns is dictated by the size of the traditional cord wood fuel source and the labor intensive nature of the firing process which lends itself to large batch sizes. As a result, conventional wood-fired kilns are not practical for use by amateur and small scale production users.